Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$34.63	6.102%	$36.7431	$36.74	$36.75	$36.70
Purchase #2	$181.54	5.660%	$191.8152	$191.82	$191.80	$191.80
Purchase #3	$59.78	8.593%	$64.9169	$64.92	$64.90	$64.90
Purchase #4	$36.42	3.773%	$37.7941	$37.79	$37.80	$37.80
Purchase #5	$156.44	4.152%	$162.9354	$162.94	$162.95	$162.90
Purchase #6	$145.91	6.164%	$154.9039	$154.90	$154.90	$154.90
Purchase #7	$27.90	11.765%	$31.1824	$31.18	$31.20	$31.20
7 purchase totals =	$642.62		$680.2910	$680.29	$680.30	$680.20